Servo positioners are generally used for positioning a mechanical member such as a shift lever, for example, for shifting the clutch mechanism of a marine vessel between the several positions, namely, neutral, forward, or reverse. When a fluid pressure, piston-operated positioner device is employed for this purpose, there is a possibility of fluid pressure failure, in which event it becomes necessary to operate the shift lever manually. Manual operation of the shift lever may be difficult due to frictional resistance or dash pot action of the piston or pistons of the positioner device. In order to permit shifting under these adverse conditions, it may be necessary to provide special mechanism for releasing the connection between the positioner device and the shift lever.